Purpose: Aims to determine the variability of ffERG measurements in patients with clinically stable birdshot chorioretinopathy (BCR).Methods: Repeatability coefficients (RC) of ffERG amplitudes and implicit times were calculated from 11 BCR patients. Jackknife resampling estimated 95% confidence intervals of each ERG parameter's RC and the percentage change explained by variability alone was calculated.Results: Intra-visit variability in ffERG parameters was lower than inter-visit. Intravisit RCs demonstrated that for intravisit ERG testing, there was less than 30% variation in ERG amplitude for most parameters. For inter-visit ERG testing, a greater than 40% reduction in ERG amplitude may be clinically meaningful for 6 of 8 ERG parameters. Photopic single flash responses have <2 msec of test-retest variability both within and across visits.Conclusions: A 40% reduction in ERG amplitude and/or a delay of >2 msec in the photopic single flash response may be suitable criteria for meaningful change in BCR patients.
Keywords: Electroretinography; birdshot chorioretinopathy; test variability.